This feels right to me, but I wonder what he was thinking of when he said “problem”. For me life is most effortless when I’m working on math or cs problems/puzzles but I sometimes get this guilty feeling that I “should” be working on a problem that is useful to the rest of the world.
Yeah, there's problems, like puzzles and mysteries, and then there's difficulties, and there's no sharp dividing line but the difficulties are less fun. And are also called problems.
So far as moral duty goes, play to your strengths, you're at your best when having fun. This conveniently evaluates to "do what you like". It's not perfectly true, but you can get away with it, blamelessly. Nobody needs you miserable, usually. Then there's the wrinkle where the importance of something to humanity (or even the promise of a large cash reward) may make it fun ... if you happen to feel that way.
